Prior automatic splicing apparatus, as shown in FIG. 1, detects the tension of the splicing apparatus' out-side by a detector 41, and controls a brake 3b of the first unwinder core 3a and a brake 4b of the second unwinder core 4a through a tension amplifier 42 so that the web tension at the time of ordinary running can be kept constant.
When splicing, the tension control is cut once; the unwinder core (old core) 3a is stopped by heavy braking at the same time; and the air pressure of an air accumulation roll unit 45 is fixed to the stroke-end by an air cylinder 46. When the speed of the unwinder core 3a decreases, the accumulation roll unit 45, pulled by the tension of a web (material) 7 via rollers such as roller 40, starts moving toward a direction where a cylinder stroke is shortened. Thus, while the unwinder core 3a make a speed-decrease/stop, and web splicing is over, the web accumulated in the accumulation unit is supplied.
The air pressure of the air cylinder 46 is gradually increased, as the web splicing work is over. At this time, the brake 4b of the unwinder core (new core) 4a is weaker; the accumulation roll unit 45 decreases its speed as the air pressure in the cylinder increases, and moves to the contrary direction (the direction in which the cylinder stroke is prolonged) finally to the stroke end.
The unwinder core 4a, due to the deceleration of the accumulation roll unit 45, starts feeding the web by a length equivalent to a difference between the volume of the line's pull-out and the volume of the accumulation sections's feed-out. At this time, to support acceleration of the unwinder core 4a, a motor 49 of a capstan roll 48 is driven. The motor 49 is stopped when the acceleration of the unwinder core 4a ends. The tension control of the unwinder core 4a resumes and the normal running starts.
In the conventional automatic web splicing apparatus, it has been impossible to hope for high accuracy and, high responsive tension, because the web tension of the out-side of the web splicing apparatus is controlled by the brake force of the unwinder core which has large inertia and because the web span up to a tension detector 41 is very large, and mechanical loss caused by intermediate roll's friction and the effect of acceleration and deceleration of the line speed piled up over the tension.
In the conventional automatic splicing apparatus, the web tension is not controlled while the tension control is stopped, and therefore, the various such problems as mentioned below cannot be avoided.
While decelerating the speed of the unwinder core (old core), the web tension is kept by the "push pressure" of the accumulation roll unit 45 which is brought by the air cylinder 46. It is impossible to change the air pressure of the air cylinder 46 in a moment from the state of normal running to the state as set for web splicing.
In addition, the inertia of the air cylinder together with the inertia of the accumulation roll unit 45 causes disturbance to a large extent against the web tension. The quicker the speed of the latter part process after splicing becomes, the more serious a problem it will be.
And, while accelerating, the acceleration torque to accelerate the unwinder core becomes a fluctuation of the tension. The motor 49 is driven during acceleration to supplement a certain volume of torque. But, as there exist webs of various diameter and/or width around the new core, the supplement is nothing but a supplement. Furthermore, the new core's acceleration time is determined by the accumulated tension and the unwinder core inertia, and therefore, it is required to rise the tension of the accumulation unit for rising the new core acceleration in a short period of time. But, this rise-time will become unstable.
Due to causes mentioned above, it has been impossible for the conventional web splicing apparatus to keep away from the occurrence of a large fluctuation of tension while performing web splicing at a high speed, and this tension fluctuation has caused outbreak of web snaps and/or creases on the web in the latter course of process after splicing. Therefore, it has been impossible to rise the process speed of the whole line.